Nickel base cast alloys have been extensively used for turbine parts and component designs requiring high temperature strength and corrosion resistance, for use at temperatures in excess of 1800.degree. F. (982.degree. C.). Single crystal casting techniques have been developed for the manufacture of gas turbine blades and permit alloys compositions to be further optimized for high temperature strength by removal of grain strengthening elements such as carbon, boron and ziconium, which adversely affect heat treatability. The primary strengthening mechanism of nickel base super alloys cast in single crystal components, is the formation of the intermetallic gamma prime phase, Ni.sub.3 (Al, Ti). The stress-rupture life of such single crystal components, is a function of the volume fraction of fine gamma prime particles in the microstructure.
Removal of grain boundary strenghtening elements such as B, Zr, Hf, and C (which are also melting point depressants) resulted in an increase in the incipient melting point from about 2265.degree. F. (1240.degree. C.) to about 2425.degree. F. (1330.degree. C.). This increase was sufficient to permit the originally cast gamma prime phase to be almost completely solutioned and then reprecipitated as fine particles for maximum strength. The complete solutioning and reprecipitation of the gamma prime resulted in single crystal alloys with 25.degree.-100.degree. F. (38.degree. C.) temperature improvement in the 30 to 50 KSI stress-rupture life range over prior alloys.
Rhenium additions to nickel-base super alloys has been found to be a successful alloying approach to achieve further high temperature strength improvements for blading alloys.
It is an object of my present invention to provide a rhenium containing single crystal nickel-base alloy article having a combination of improved stress-rupture life, metallurgical phase stability and good environmental resistance. These and other objects are realized by my present invention as will be appreciated from the following description of my invention.